Silicon carbide (SiC) which is expected as a next-generation power semiconductor device material has physical property values such as a band gap which is three times that of silicon (Si), a breakdown electric field strength which is about ten times that of silicon, and thermal conductivity which is about three times that of silicon. If this property is utilized, it is possible to realize a power semiconductor device capable of operating at a high temperature with ultralow loss.
There are several high withstand voltage semiconductor devices using such properties of silicon carbide, but a double implantation MOSFET (hereinafter, referred to as DIMOSFET) in which a well region and a source region are formed by ion implementation is well known. Since a DIMOSFET uses a planarization process capable of forming a channel with high accuracy by an ion implantation method, manufacture thereof is easy. Since gate driving is voltage control, power of a drive circuit can be decreased. Thus, the DIMOSFET is suitable for a parallel operation.
However, a self-alignment process by thermal diffusion performed in manufacture of a silicon MOSFET cannot be used in silicon carbide. Therefore, when a channel region of a silicon nitride MOSFET is formed, a well region and a source region for determining a channel length are individually subjected to ion implantation using two masks. In order to reduce ON resistance, it is necessary to reduce resistance of a channel portion. However, the channel length is deviated due to misalignment when the channel length is defined using two masks and thus microfabrication is prevented.
In manufacture of a trench MOSFET by forming a trench by dry etching and providing a MOS channel at a sidewall thereof, a region in which the trench and a p-well region overlap becomes a channel. Thus, the channel length does not depend on alignment accuracy of the masks. Accordingly, by changing ion implantation depth of the p-well region and the n+ source region, it is possible to easily realize a short channel. However, since an excessive electric field is applied to a gate insulating film of the bottom and end of the trench, there is concern about insulation breakdown of the gate insulating film.